1. Field of the Invention
The present invention relates to a magnetic memory device being a nonvolatile solid-state memory using magnetoresistive elements, and to a manufacturing method thereof.
2. Description of Related Art
In recent years, semiconductor memory devices being solid-state memories have widely been used for information equipment and the like. The kinds of the semiconductor memory devices are various such as a dynamic random access memory (DRAM), a ferroelectric random access memory (FeRAM), and an electrically erasable programmable read-only memory (EEPROM). The characteristics of such semiconductor memory devices have both merits and demerits, and it is difficult for the conventional semiconductor memory devices to meet all of the specifications required by the present information equipment.
Accordingly, a magnetic memory device (a magnetic random access memory (MRAM)) using magnetoresistive elements has been researched and developed in recent years. Because the magnetic memory device uses magnetic films for storing information, the magnetic memory device has nonvolatility being a feature such that the stored information is not erased even if the power supply to the magnetic memory device is turned off. And the magnetic memory device is expected to meet all of the specifications required by various pieces of information equipment with respect to various characteristics such as a recording time, a readout time, a recording density, the capable number of times of rewriting, and electric power consumption.
The magnetic memory device is provided with the magnetoresistive elements as its memory cells. Spin dependent tunneling magnetoresistive elements (TMR elements) are suitably used as such magnetoresistive elements. The TMR element has the basic structure composed of two magnetic layers and a thin non-magnetic layer put between them for storing information. The magnetoresistive ratio (MR ratio) of the TMR element is larger than that of other magnetoresistive elements, and the value of resistance of the TMR element can be set at a value within a range from several kxcexa9 to several tens kxcexa9 which is the most suitable value as the value of resistance of a memory cell of the magnetic memory device. Consequently, the TMR elements are generally used as memory elements of the magnetic memory device.
The value of the resistance of the TMR element differs in the case where the pieces of magnetization of the magnetic layers with the non-magnetic layer put between them are parallel to each other (see FIG. 14A) and in the case where the pieces of magnetization of them are anti-parallel to each other (see FIG. 14B). Accordingly, the two states can be stored as logical values xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d, respectively. The states of the logical values xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d can be stored by, for example, fixing the direction of the magnetization of one of the two magnetic layers and by changing the direction of the magnetization of the other of the two magnetic layers by external magnetic fields. The operation is the so-called information writing operation. The method is known which uses the magnetic fields generated by an electric current flowing through the wiring disposed in the vicinity of the TMR element for changing the direction of the magnetization.
Then, the value of the resistance of the TMR element is obtained by detecting the voltage or the current of the TMR element. The states of the logical values xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d can be distinguished on the basis of the value of the resistance. The operation is the so-called information readout operation. To put it more concretely, the following two detection methods are known: the absolute detection method distinguishing the states of the logical values xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d on the basis of the absolute value of the resistance, and the differential detection method reading the states of the logical values xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d by applying a magnetic field weaker than that at the time of writing to cause the magnetization reversal of only the magnetic layer having a smaller coercive force.
The TMR element using the so-called in-face magnetization films magnetized in the direction parallel to the surfaces of the magnetic layers as shown in FIGS. 14A and 14B has the following problem in the case where the size of the element is made to be small. That is, when the size of the TMR element is made to be small, demagnetizing fields (self attenuation magnetic fields) are generated in the magnetic layers and the curling of the magnetization is also generated at the end surfaces thereof. Thereby, the magnetization direction of the magnetic layer to record and hold information is not determined in a fixed direction to be instable. Consequently, it becomes impossible for the TMR element to hold the information owing to the decrease of the magnetoresistance ratio (MR ratio) thereof caused by the instability of the magnetization direction and the like. Hence, the TMR element of the type of in-face magnetization has the limitations of the miniaturization and the large scale integration of the memory device using the TMR elements owing to the impossibility of the holding of information in case of making the sizes of the TMR elements too small.
U.S. Pat. No. 6,219,275 discloses a TMR element using the so-called perpendicular magnetic anisotropy film in which magnetization is made in the direction perpendicular to the surfaces of magnetic layers (see FIGS. 15A and 15B) for solving the above-mentioned problem. The perpendicularly magnetized TMR element does not generate large demagnetizing fields even if the size of the TMR element is made to be small, and can hold information stably. Consequently, the perpendicularly magnetized TMR elements can constitute a magnetic memory device smaller in size and more highly integrated than that composed of the TMR elements of the type of the in-face magnetization.
In the case where a magnetic memory device is composed by the use of the above-mentioned TMR elements, it is general to adopt the structure in which the TMR elements are laminated on metal oxide semiconductor field effect transistors (MOSFET""s). To put it concretely, the magnetic layers of the TMR elements are connected with the drain regions of the MOSFET""s through conductive members such as metal plugs.
A conventional magnetic memory device has the problem in which it is difficult to form non-magnetic layers located between magnetic layers to be flat. In such a case, the problem may be produced in which magnetization directions of the upper and the lower magnetic layers of a memory cell in such a magnetic memory device cannot be formed in an ideally parallel state or an ideally anti-parallel state. In particular, in the case where the tunneling barrier layer of a TMR element is not flat, unevenness of film thickness is produced to generate a leakage current. The leakage current causes the decrease of the MR ratio in turn. Moreover, in the case where the magnetization directions of the upper and the lower magnetic layers is not in the ideally parallel state or the ideally anti-parallel state, the spin polarizability of the interfaces of the tunneling barrier layer decreases also to decrease the MR ratio. That is, it becomes impossible to obtain stable changes of the magnetoresistance of the TMR element.
Accordingly, the present invention aims to provide a magnetic memory device having the following characteristics, and a manufacturing method thereof. That is, the surface roughness of the magnetoresistive elements laminated on the conductive members of the magnetic memory device is small, and the magnetic layers and the non-magnetic layers of the magnetic memory device are flat. Moreover, in the magnetic memory device using TMR elements particularly, the leakage current is suppressed, and the MR ratio thereof is high.
A feature of the present invention exists in a point that in a non-volatile magnetic memory device including a magnetoresistive element composed of a first and a second magnetic layers being magnetized chiefly in a direction perpendicular to film surfaces and a non-magnetic layer located between the first and the second magnetic layers, the magnetoresistive element being connected with a conductive plug, wherein the magnetoresistive element is disposed at a position distant from a position right above the plug in a plane, and a local connect is provided for connecting an upper surface of the plug and a lower surface of the magnetoresistive element.
It is preferable that the local connect is made of titanium or titanium nitride.
The plug may be made of tungsten or copper, and may be formed to penetrate the insulating film substantially perpendicularly.
It is preferable that the magnetic memory device further comprises a bit line located above the magnetoresistive element for applying a magnetic field to the magnetoresistive element and the magnetic field is applied in an easy axis direction of magnetization of the magnetic films.
It is preferable to locate the magnetoresistive element at a position shifted from a principal wiring part of the bit line in a plane.
It is preferable that the non-magnetic layer is an insulator.
It is preferable that the magnetic memory device further comprises wiring for applying a magnetic field in the in-face direction to the magnetic films to apply a magnetic field generated by the wiring and the magnetic field generated by the bit line and thereby the magnetization of at least one of the first and the second magnetic films is reversed.
Another feature of the present invention exists in a manufacturing method of a non-volatile magnetic memory device including a magnetoresistive element composed of a first and a second magnetic layers being magnetized chiefly in a direction perpendicular to film surfaces and a non-magnetic layer located between the first and the second magnetic layers, the magnetoresistive element being connected with a conductive plug, the method comprising the steps of: forming the plug; forming a conductive local connect contacting with an upper surface of the plug and extending to a horizontal direction; and forming the magnetoresistive element at a position distant from a position right above an upper surface of the plug in a plane on the local connect.
It is preferable that the local connect is formed by use of titanium or titanium nitride.
The plug may be made of tungsten or copper, and may be formed to penetrate the insulating film substantially perpendicularly.
It is preferable to include the step of forming a bit line above the magnetoresistive element for making an electric current flow therethrough for applying a magnetic field to the magnetoresistive element.
It is preferable to form the bit line at a position shifted from a position right above the magnetoresistive element in a plane.